How to Calculate Quantities of Cement, Sand and Aggregate for Nominal Concrete Mix (1:2:4)?

How to Calculate Quantities of Cement, Sand and Aggregate for Nominal Concrete Mix (1:2:4)?

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ahujaconcrete

28August14

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Mix design is a process of determining the right quality materials and their relative proportions to prepare concrete of desired properties like workability, strength, setting time and durability.

While following a mix design is advised to optimise the material consumption, it is not possible at site to always come up with Mix design. Nominal mix concrete is prepared by approximate proportioning of cement, sand and aggregate to obtain target compressive strength.

Material requirement for producing 1 Cum of Nominal Concrete Mix

The following are the materials required to produce 1 Cum of Concrete of a given Nominal Mix Proportion

Grade of Concrete

Nominal Proportion

Cement (bag)/cum

Sand (in cft)

Aggregate (in cft)

M15

1:3:6

4.5

16.04

32.07

M20

1:2:4

6

14.98

29.96

M25

1:1.75:3.5

6.75

14.75

29.14

M30

1:1.5:3

7.5

14.06

28.11

Incase you want to convert the requirement of Sand and Aggregate in Cum; 1 Cum = 35.31 Cft

Eyeopener : Many popular blogs claim M20 nominal mix as 1:1.5:3 ,however we strongly differ by same.Through this blog,we are also trying to address the same myth which is being carried forward since last 4 decades.

The reason being: With constant research and development in the field of cement technology and its manufacturing process ,a M20 mix of “1:1.5:3″(by volume) would be too rich, over engineered and uneconomical (~7.5 bags of cement per cum) and will ultimately result into a M30 concrete and above (IS:456 too have the minimum cement/cementitious content of 06 bags for M20). As the latest generation of 53 grade OPC cement is ultimately giving a strength of 65 to 70 MPa at 28days, 1:2:4 will give a strength of M20.

A detail procedure to calculate the cement bags required for 1: 2 :4 mix (~6 bags of cement per cum) is shown below.

The DLBD (Dry Loose Bulk Densities) method is an accurate method to calculate cement, sand and aggregate for a given nominal mix concrete. This gives accurate results as it takes into account the Dry Loose Bulk Densities of materials like Sand and Aggregate which varies based on the local source of the material

For calculation, We consider a nominal concrete mix proportion of 1:2:4 (~M20).

Step-2: Convert Volume requirement to weights

To convert Sand volume into weight we assume, we need the dry loose bulk density (DLBD). This density for practical purposes has to be determined at site for arriving at the exact quantities. We can also assume the following dry loose bulk densities for calculation.

DLBD of Sand = 1600 kgs/cum

DLBD of Aggregate = 1450 Kgs/Cum

So, Sand required = 0.072*1600 = 115 kgs

and Aggregate required = 0.144*1450 = 209 kgs

Considering water/cement (W/C) ratio of 0.55

We can also arrive at the Water required = 50*0.55 = 27.5 kg

So, One bag of cement (50 Kgs) has to be mixed with 115 kgs of Sand, 209 Kgs of aggregate and 27.5 kgs of water to produce M20 grade concrete.

Cement

Sand

Aggregate

Water

1 bag (50kg)

115 Kgs

209 Kgs

27.5 Kgs

Step-3: Calculate Material requirement for producing 1 cum Concrete

From the above calculation, we have already got the weights of individual ingredients in concrete.

Although empirical method is easy to use in determining the materials requirement for Nominal Concrete mix, it sometimes doesn’t give accurate results as it doesn’t take into factor the local variations in the materials.

Let’s design M20 grade concrete. Ratio for M20 concrete is 1 : 2 : 4

Step-1: Calculate the Volumes of material required in 1 Cum concrete

The dry volume of concrete mixture is always greater than the wet volume. The ratio of dry volume to the wet volume of concrete is 1.54.

So 1.54 Cum of dry materials (cement, sand and aggregate) is required to produce 1 Cum of concrete

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We are a well-known manufacturer of Ready Mix Concrete. Set up in 2007, the company has grown from strength to strength. Cutting-edge technology and innovation are the key factors that drive us, and have brought us to the forefront despite stiff competition.
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